1. Technical Field
The present invention relates to a semiconductor device including an electric fuse.
2. Related Art
In recent years, there has been proposed a new method of cutting off an electric fuse, which is called a “crack assist type process.” In this method, when an electric fuse is cut off, the structure of the electric fuse and the voltage application to the electric fuse are controlled so as to forcibly cause the conductive material of the electric fuse to flow out at a part of the electric fuse and to flow into the insulating film existing in the vicinity of the conductive material. By doing so, the balance between the material flowing out and being supplied is upset, and a large cut-off portion is formed in another area. In this manner, the probability of a reconnection of a cut-off electric fuse can be significantly reduced, and a desirable cut-off state can be maintained. (for example, see Japanese Laid-open patent publication NOs. 2007-73624, 2007-305693 and 2007-305939).
Japanese Laid-open patent publication NO. 2007-73624 discloses a structure in which a fuse is folded back. With this structure, fuse materials at portions where the fuse is folded back are apt to be heated so as to prompt a cut-off while allowing the fuse to be cut off at other portions, thereby appropriately keeping the cut-off state of the cut-off fuse.
Japanese Laid-open patent publication NOs. 2007-305693 and 2007-305939 disclose an electric fuse including a lower-layer wiring, an upper-layer wiring and a via connecting these layer wirings. With this configuration, for example when a conductor, which is formed from the upper-layer wiring constituting the electric fuse, is ejected outward, a conductor of the via is moved with the movement of the conductor such that a cut-off portion is formed in the via. In this manner, by forming the cut-off portion in the via, it is possible to prevent the electric fuse from being reconnected after the cut-off of the electric fuse.
In addition, Japanese Laid-open patent publication NOs. H-6-140510, 2007-5424, 2005-39220 and 2005-197416 also disclose a structure in which a fuse is folded back. Specifically, Japanese Laid-open patent publication NOs. H-6-140510, 2007-5424 and 2005-39220 disclose a conventional electric fuse in which a material composing the fuse is melted and cut-off by the flow of a current through the fuse. With this configuration, by folding back cut-off portions of the fuse, a current is concentrated on a curved portion of a fuse link, which results in facilitation of the melting of the fuse material. Japanese Laid-open patent publication NO. 2005-197416 discloses a structure in which a fuse is cut-off by a laser. With this structure, by folding back the cut-off portion of the fuse, it is possible to improve the establishment of the cut-off even if the laser beam deviates.